Present invention relates to a printing apparatus and method and, more particularly to a printing apparatus and method for printing on a recording medium, in accordance with an ink-jet printing method.
Recently, printheads mounted on a printing apparatus which performs printing in accordance with the ink-jet printing method are manufactured using a thin-film forming process for semiconductors, a microprocess technique and the like, so that they are small-sized, and can be provided with low prices. One of these printheads, an exchangeable type printhead, is known as an ink cartridge in which a printhead device for discharging ink as printing material is integrally assembled with an ink tank for supplying the ink to the print-head device.
FIG. 8 shows the structure of a conventional ink-jet printer IJRA. In FIG. 8, a carriage HC is engaged with a spiral groove 5005 of a lead screw 5004 which rotates via driving force transmission gears 5011 and 5009 interlocking with forward/reverse rotation of a driving motor 5013. The carriage HC has a pin (not shown) and it is reciprocally moved in directions represented by arrows a and b. The carriage HC has a disposable type ink-jet cartridge IJC which integrally comprises a printhead IJH and an ink tank IT. The ink-jet cartridge IJC can be easily attached/removed. A paper bail 5002 presses a printing sheet P against a platen 5000 along the moving direction of the carriage. Photocouplers 5007 and 5008 are home position detecting members for confirming the existence of lever 5006 of the carriage in this area and changing over the rotational direction of motor 5013. A support member 5016 supports a cap member 5022 for capping the front surface of the printhead IJH. A suction member 5015 performs suction-restoration of the printhead the inside of the cap member 5022 via a cap inner opening 5023. Member 5019 allows a cleaning blade 5017 to move in a back-and-forth direction. A main body support plate 5018 supports the member 5019 and the cleaning blade 5017. It is apparent that any well-known cleaning blade is applicable to the printer of the embodiments. Numeral 5021 denotes a lever for starting the sucking operation of the suction-restoration. The lever 5021 moves along the movement of a cam 5020 engaged with the carriage. A well-known transmission mechanism such as change-over of a clutch controls a driving force from the driving motor.
When the carriage is at the home position area, a desired processing such as capping, cleaning and suction-restoration is executed at its corresponding position by the lead screw 5005. The timing of any of these processings is not limited to the printer of the embodiments, if a desired processing is performed at a well-known timing.
The motor 5013 controls the conveyance of the printing sheet P in a direction vertical to the direction of the movement of the carriage HC. The printing sheet P is conveyed when the printhead IJH of the ink-jet cartridge IJC does not perform printing. Note that some ink-jet printers use motors respectively for horizontal movement (for moving the carriage HC) and for vertical movement (for conveying the printing sheet P), in place of the motor 5013.
Off-the-shelf printers usually have a specification corresponding to a monochromatic printhead-integrated ink-jet cartridge of detachable type, because monochromatic printers occupy the major market. In a memory of such printer, a buffer for temporarily storing data from a host computer, an image buffer for print control, and a work area are arranged for monochromatic printing, and the memory allocation is generally static.
FIG. 9 shows the flow of data from a host computer to a printhead-integrated ink-jet cartridge. As shown in FIG. 9, data sent from a host computer 21 is temporarily stored in a reception buffer 22 of the printer. The stored data is converted into image data in a print-control work area 23, in accordance with necessity, and transferred to an image buffer 24. In this conversion, character modification, expansion of compressed data and the like are executed. On the other hand, when image data is directly inputted from the host computer 21 to the reception buffer 22, the image data is directly transferred from the reception buffer 22 to the image buffer 24. Thereafter, when the status of the image buffer 24 becomes ready for printing, i.e., data corresponding to the number of the nozzles of the printhead is stored into the image buffer 24, the data is transferred to a printhead 25 integrated in the ink-jet cartridge, and printing is performed.
FIG. 10 shows the memory allocation of the conventional monochromatic printer. As shown in FIG. 10, the memory is allocated to a reception buffer area 26 for receiving data from the host computer, an image buffer area 27 and a print-control work area 28 for print control. The memory capacity of the image buffer area 27 may be at least for storing data corresponding to the maximum printing width of the printhead, i.e., an effective printing width in one scanning of the carriage of the printhead. However, for the purpose of high-speed printing, the image buffer area 27 may be ensured for storing the print data corresponding to printing width, printed by a plurality of scannings of the carriage, so as to store data for next scanning while the printhead performs current printing operation.
This memory allocation may also be applied to a color printer.
FIGS. 11A and 11B show the memory allocation in a color printer (FIG. 11A) and the nozzle arrangement of a printhead for color printing (FIG. 11B).
In case of a color printer, four inks, i.e., black, yellow, magenta and cyan color inks are generally employed to represent a color image based on color print data. Comparing FIG. 11A and FIG. 10, there is no difference in the memory structure between the monochromatic printer and the color printer, though a reception buffer 29 and a print-control work area 31 are different in capacity depending upon color/monochromatic printing. Regarding the image buffer, the color printer needs four image buffers 30BK, 30Y, 30M and 30C, corresponding to the black, yellow, magenta and cyan color inks actually discharged from the printhead.
As a typical example in FIG. 11B, the printhead for ink-jet color printing has 24 yellow-ink nozzles 32Y for discharging yellow ink, 24 magenta-ink discharge nozzles 32M, 24 cyan-ink discharge nozzles 32C and 64black-ink discharge nozzles 32Bk, aligned in a direction where a recording medium such as a paper sheet is conveyed (subscanning direction). The interval between the nozzles is corresponding to eight nozzles. Print data stored in the image buffers 30BK, 30Y, 30M and 30C are outputted to the printhead, and the color inks respectively based on the print data are discharged from the corresponding nozzles. As this printhead forms a multi-color image with four color inks, the different color inks are overlaid by conveying the recording medium in the subscanning direction.
In this manner, the physical specification of the color printhead requires image buffers for four color data.
Note that in case of a monochromatic printer, it is unnecessary to mount nozzles for a plurality of color inks on the monochromatic printhead. The monochromatic printhead may comprise nozzles for single color ink, therefore, the number of nozzles can be increased to, e.g., 128 nozzles, to improve throughput and printing quality in printing based on monochromatic data.
Currently, in addition to the monochromatic printers and color printers as described above, printers for both monochromatic printing and color printing have appeared. In printers of this type, a printhead-integrated ink cartridge can be exchanged for another kind of printhead-integrated ink cartridge (e.g., a monochromatic ink cartridge is exchanged for a color ink cartridge). Hereinafter, a printer of this type will be referred to as "add-on printer".
However, the conventional add-on printer has a memory allocation on the assumption of color printing, since the storage amount in color printing is larger than that in monochromatic printing. That is, even when a monochromatic ink cartridge is mounted for monochromatic printing, or even when a color ink cartridge is mounted but monochromatic print data is received from a host computer, the memory allocation within the memory is not for monochromatic printing which is actually performed, but for color printing. This memory allocation cannot attain efficient memory use.
This problem will be described in detail with reference to FIGS. 12A and 12B. FIG. 12A shows the use of the memory in a case where color print data is sent from the host computer; and FIG. 12B, the use of the memory in a case where monochromatic print data is sent from the host computer. In these figures, a hatched portion indicates an actually used memory area. In FIG. 12B, the hatched portions are smaller in the respective memory areas than in those of FIG. 12A, which means that areas for color print data are not used in the reception buffer, the control area and the image buffer. This status is the same whether the attached printhead-integrated ink cartridge is a monochromatic ink cartridge or a color ink cartridge.
As it is apparent from the above description, the memory allocation in the add-on printer is static regardless of the type of ink cartridge. This cannot attain efficient memory use to improve throughput and sufficiently ensure a download area, especially upon printing based on monochromatic print data, due to occurrence of wasteful unused memory area.